Self-transducing ultrasonic amplifier

ABSTRACT

There is disclosed an ultrasonic amplifier for use with microwave signals which does not require transducer elements. A piezoelectric semiconductor element containing current carriers cooperates with a pair of waveguide sections. The microwave signal at the end of one of these sections generates an acoustic signal in the piezoelectric semiconductor element which is amplified by drifting current carriers as it travels down the element. The acoustic signal thereafter excites an electromagnetic signal at the start of the other waveguide section.

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1111 3,563,080 iviioolNu K11 3.406350 10/1968 Newell 330/55 3,409,847 11/1968 Nanney 330/5 3,440,550 4/1969 More..... 330/55 3,435,250 3/1969 Reggia..... 330/55 3,458,831 7/1969 Veilex .1 330/55 72] Inventor Ronald R. Troutman Rustic Drive, Essex Junction, Vt. 05452 [21] Appl. No. 844,130 [22] Filed July 23,1969 [45] Patented Mar. 2, 1971 [54] SELF -TRANSDUCING ULTRASONIC AMPLIFIER Claims, 4 Drawing Figs.

[52] 11.5. CI 330/55, 333/30, 330/53 [51 Int. Cl l ll03f3l04 [50] Field ofSearch 330/5.5,5; 333/30 [56] References Cited UNITED STATES PATENTS 3,105,966 /1963 Jacobsen 333/ 3,289,090 11/1966 Shiren 330/55 3,292,114 12/1966 Mason.... 330/55 3,321,647 5/1967 Tien 330/55 Zipa/ Primary Examiner-John Kominski Assistant Examiner-Darwin R. Hostetter Attorneys-R. l. Tompkins and L. l. Shrago ABSTRACT: There is disclosed an ultrasonic amplifier for use with microwave signals which does not require transducer elements. A piezoelectric semiconductor elemen't containing current carriers cooperates with a pair of waveguide sections. The microwave signal at the end of one of these sections generates an acoustic signal in the piezoelectric semiconductor element which is amplified by drifting current carriers as it travels down the element. The acoustic signal thereafter excites an electromagnetic signal at the start of the other waveguide section.

SELF-TRANSDUCING ULTRASONIC AMPLIFIER The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates generally to ultrasonic apparatus, such as, acoustic amplifiers and delay lines and, more particularly, to a solid-state microwave amplifier of the travelmg wave type.

In the socalled microwave ultrasonic amplifier, an acoustic signal in the microwave frequency range is propagated through a piezoelectric semiconductor. The acoustically induced compressions and rarefactions of the crystal lattice structure cause alternate positive and negative electric charges to be created as a consequence of the piezoelectric coupling constant. If the piezoelectric semiconductor contains proper impurity ions, an electron drift may be initiated within the crystal with the application of an appropriate electric potential. If these electrons drift colinearly with the acoustic phonons at a speed just in excess of the velocity of sound in the material, then the phonon wave will be amplified in a manner analogous to the amplification process occurring in traveling wave tubes.

A description and more detailed operation of this general type of microwave ultrasonic amplifier may be found in an article by A. R. Hudson, I. H. McFee and D. L. White, appearing in the Physical Review Letters," Volume 7, No. 6, pages 237 to 239,0fSept. 15, I961.

Besides performing as an amplifier for acoustic signals in the microwave frequency range, the above arrangement may also be used as a delay device for imparting a time delay to microwave signals. The delay, of course, is realized because of the relatively low velocity of propagation of acoustic signals as compared to their electromagnetic wave energy counterparts.

One of the problems associated with the design and operation of these solid-state devices is that of coupling the microwave signal to the acoustic wave in the piezoelectric semiconductor. Conventional transducers cannot be readily used because at the frequencies involved the dimensions of these transducers must be extremely small.

It is accordingly a primary object ofthe present invention to provide a solid-state acoustic amplifier for use with signals in the microwave frequency range which does not require separate transducers for coupling the signal into and out of the solid-state device.

It is another object of the present invention to provide a microwave ultrasonic amplifier wherein the signal to be amplified is coupled directly into the amplifying medium without an intervening transducing element.

Another object ofthe present invention is to provide a solidstate signal delay device for use in the microwave frequency region which employs a self-transducing mechanism.

Otherobjects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

FIG. I illustrates one embodiment of the present invention for use in a signal feed-through system;

FIG. 2 illustrates the mode of operation of the apparatus where the optic axis of the piezoelectric semiconductor element is perpendicular to the paper;

FIG. 3 illustrates the situation where this axis is in the plane of the paper; and

FIG. 4 is an alternative embodiment of a more compact construction.

Briefly and in somewhat general terms, the present invention accomplishes the objects of invention enumerated above by making use of the fact that if high frequency electromagnetic radiation is directed at a piezoelectric element, the oscillating electric field corriponent will generate an acoustic wave at the boundary surface of this element. This acoustic wave will travel through the piezoelectric element and the element, itself, need not oscillate as a complete resonant structure. When this acoustic signal reaches another boundary surface of the element, it will be transformed back to an electromagnetic wave which may be sensed, for example, by an appropriate detector.

In the present invention, the microwave signal is similarly introduced into the piezoelectric element, that is, the open end of a waveguide structure is placed directly against a boun dary surface of the piezoelectric element so as to excite an acoustic signal in the manner above described. A second waveguide section is placed against a remote boundary surface at a location where the emerging acoustic signal after its passage through the piezoelectric element excites an electromagnetic wave energy signal.

Referring now to FIG. 1 of the drawings which illustrates a feed-through arrangement, it will be seen that the apparatus consists of a piezoelectric semiconductor element 1 having metallic electrodes 2 and 3 applied to a pair of opposite planar end surfaces 4 and 5 which are orientated at an acute angle with respect to the longitudinal axis of symmetry of the piezoelectric element. These surfaces, which also serve as acoustic signal reflecting means, are parallel and, in the illustration shown, are at a angle with this axis.

The piezoelectric semiconductor element 1 may, for example, be made ofcadmium sulfide or other suitable II-VI compounds. Some of the lIl-V compounds are also appropriate. Typical of the satisfactory ll-VI compounds are CdS, ZnO and lithium metaniobate.

In the case where the piezoelectric member is a II-Vl compound, the III elements may be introduced to provide donor impurities, these elements serving as replacements for the II elements. Likewise, elements from the VII compounds may be utilized as donor replacements for the VI elements. In the first case just mentioned, 8, AI, Ga, ln, and TI may be used, while in the second, F, Cl, Br and I may be employed. Where the piezoelectric element or the substrate material is lithium metaniobate, the II elements may serve as donors.

Cooperating with the piezoelectric semiconductor element 1 are a pair of waveguide sections 6 and 7. Section 6, the input section, terminates at the bottom surface of piezoelectric element 1 at a location adjacent end face 4. Section 7, the output section, terminates at a similar location adjacent face 5.

It will be appreciated that when a microwave signal is propagated through input signal section 6 towards piezoelectric element 1, the electric field present at the terminating boundary will generate an acoustic signal ofthe same frequency thereat. To increase the efficiency ofthis conversion operation, the mode of propagation within input section 6 should be such that an intense electric field region exists at the terminating region. The acoustic signal so produced travels through the thickness of the piezoelectric semiconductor element 1 in a direction parallel to the longitudinal axis of input waveguide section 6 until it strikes face 4. At this surface it is reflected and directed down the piezoelectric element 1 parallel to its longitudinal axis of symmetry. Here, it is again reflected and directed along the longitudinal axis of symmetry of output waveguide section 7. Because of the reversible nature of the phenomenon which originally created the acoustic signal from the impinging electromagnetic wave energy signal, an electromagnetic wave is now produced at the beginning of waveguide section 7, and this wave thereafter propagates through this section.

In the case where DC piezoelectric semiconductor is cadmium sulfide, for example, when the electric field 6 associated with the electromagnetic wave is applied parallel to the optic axis x of the element, a longitudinal acoustic wave will be generated whose deformation p. and direction of propagation will be parallel to this axis. In the case where the electric field is applied perpendicular to the optic axis, a shear acoustic wave will be generated, and this wave will propagate in the direction of the electric field but its deformation will be parallel to the optic axis. Such a shear wave is used in the self-transducing amplifier of the present invention in either one or two transduction modes.

FIG. 2 schematically illustrates the case where the optic axis X of the piezoelectric semiconductor element 1 is orientated perpendicular to the plane of the paper. The longitudinal electric field component of a transverse magnetic wave traveling within waveguide 6 and striking the crystal couples into an acoustic wave having its deformation parallel to the optic axis. This shear acoustic wave reflects off inclined end face 4 and thereafter travels the length of the piezoelectric semiconductor element as a shear wave.

In FIG. 3 there is illustrated the case where the optic axis X is orientated in the plane of the paper. Here, the electric field component of the transverse magnetic wave couples into a shear acoustic wave when it interacts with the crystal surface. The mechanical deformation p. of the crystal is now in the plane of the paper. At the reflecting surface 4 this shear wave is converted into a longitudinal acoustic wave as a result of the direction of deformation, and this wave travels down the length of the crystal. It would be pointed out that the behavior of the apparatus at the other inclined end faces and the acoustic wave conditions occurring thereat are the inverse of thatjust described.

To compensate for the signal loss accompanying the transformation of the electromagnetic signal to the acoustic signal and vice versa and the attenuation of the acoustic signal, piezoelectric semiconductor element 1 may be operated in an amplifying mode. Thus, as mentioned hereinbefore, it is doped or subjected to an ion implantation process so as to place selected ion dopants in substitutional sites of the piezoelectric insulator and create current carriers. These current carriers drift down the semiconductor element 1 colinearly with the acoustic signal when an appropriate DC potential 8 is connected across electrodes 2 and 3. The polarity shown represents the condition for electron drift.

The magnitude of DC potential 8, as is well known, determines the velocity at which these current carriers drift down the semiconductor transducer element 1 and, when this move ment is at an appropriate velocity, which is slightly in excess of the velocity of sound within element 1, the acoustic signal traveling within this element will be amplified.

Thus. the electromagnetic signal excited in the output waveguide section 7 may have an amplitude ofthe same order of magnitude as the input electromagnetic Signal, or of even greater amplitude. The apparatus of FIG. I may function either as a controllable amplifier whose amplification factor is determined by bias voltage 8 or as a signal delay device because of the relatively low velocity of the acoustic signals in ,the piezoelectric semiconductor portion of the system. The

waveguide sections 10 and 11, respectively, located on the same side of the piezoelectric semiconductor element 12. To accomplish this mode of operation, end face 13 of element I2 has a reversed slope from its counterpart in FIG. 1 so that the acoustic signal reflected therefrom excites an electromagnetic wave at the entrance to output waveguide section 11. Both end faces 13 and 14 are again provided with electrodes 15 and 16 for controlling the movement of the current carriers through the piezoelectric semiconductor.

It will be appreciated that the microwave signal may be coupled to the piezoelectric semiconductor by either a waveguide section or a stripline. Also, if desired, a multiplicity of piezoelectric semiconductors of the shape shown in FIG. I or 2 may be assembled into other geometries so as to increase the overall length of the acoustic signal path without increasing the length of any of the individual piezoelectric semiconduc tor elements.

Iclaim:

1. Apparatus for amplifying and delaying microwave signals comprisin in combination:

a piezoe ectric semiconductor element containing current carriers, said element having a pair of opposite end faces which are at an acute angle with respect to the longitudinal axis of symmetry of said element;

a pair of microwave energy transmission sections, one end of each section being terminated by a surface portion of said element at a location adjacent a different end face such that the electrical field component of a microwave signal present at the end ofone of said sections excites an acoustic signal in said element that is reflected from the adjacent end face, travels down said element, is reflected from the other end face and excites a microwave signal at the end of the other transmission section; and

means for applying a DC potential across said end faces to cause said current carriers to drift down said element at a velocity. sufficient to cause amplification of any acoustic signal also traveling down said element.

2. In an arrangement as defined in claim I wherein said end faces are parallel.

3. In an arrangement as defined in claim 2 wherein said piezoelectric semiconductor element has a ,pair of parallel sides and said microwave energy transmission sections are located on opposite sides of said piezoelectric semiconductor element.

4. In an arrangement as defined in claim I wherein said opposite end faces are angularly disposed with respect to each other.

5. In an arrangement as defined in claim 4 wherein said piezoelectric semiconductor element has a pair of parallel sides and said pair of microwave energy transmission sections are located on the same side of said piezoelectric,semiconductor element. 

1. Apparatus for amplifying and delaying microwave signals comprising, in combination: a piezoelectric semiconductor element containing current carriers, said element having a pair of opposite end faces which are at an acute angle with respect to the longitudinal axis of symmetry of said element; a pair of microwave energy transmission sections, one end of each section being terminated by a surface portion of said element at a location adjacent a different end face such that the electrical field component of a microwave signal present at the end of one of said sections excites an acoustic signal in said element that is reflected from the adjacent end face, travels down said element, is reflected from the other end face and excites a microwave signal at the end of the other transmission section; and means for applying a DC potential across said end faces to cause said current carriers to drift down said element at a velocity sufficient to cause amplification of any acoustic signal also traveling down said element.
 2. In an arrangement as defined in claim 1 wherein said end faces are parallel.
 3. In an arrangement as defined in claim 2 wherein said piezoelectric semiconductor element has a pair of parallel sides and said microwave energy transmission sections are located on opposite sides of said piezoelectric semiconductor element.
 4. In an arrangement as defined in claim 1 wherein said opposite end faces are angularly disposed with respect to each other.
 5. In an arrangement as defined in claim 4 wherein said piezoelectric semiconductor element has a pair of parallel sides and said pair of microwave energy transmission sections are located on the same side of said piezoelectric semiconductor element. 